Arylene thioether polymers have heretofore been prepared mainly by a process wherein a dihalogen-substituted aromatic compound is reacted with an alkali metal sulfide in a polar organic solvent (for example, Japanese Patent Publication Nos. 3368/1970 and 25589/1978, and U.S. Pat. Nos. 3,919,177 and 4,645,826).
This reaction is represented by the following reaction formula: ##STR2## wherein Ar means an aromatic residue, M denotes an alkali metal, and X is a halogen atom.
In this preparation process, phenols and amines are formed as by-products due to the reaction of the dihalogen-substituted aromatic compound and alkali metal sulfide at an elevated temperature, and they have an undesirable effect on the polymerization degree and melt stability of the resulting polymer.
When various kinds of dihalogen-substituted aromatic compounds are separately used in the preparation process, they can be divided broadly into the following three groups by relatively evaluating them with respect to stability and reactivity in the polymerization reaction system and solubility in the polymerization solvent.
Group (G1): Standard compounds medium all in reactivity, stability and solubility, which may include, for example, those represented by the following formula: ##STR3## wherein X means a halogen atom, R denotes an alkyl group having 1-6 carbon atoms, and 1 stands for 0 or an integer of 1-4.
Group (G2): Compounds higher in reactivity compared to those of Group (G1) but unstable in the polymerization reaction system, which may include, for example, those represented by the following formulae: ##STR4## wherein X means a halogen atom.
Group (G3): Compounds poor in solubility in the polymerization solvent, which may include, for example, those represented by the following formula: ##STR5##
When copolymerization between a dihalogen-substituted aromatic compound in Group (G1) and a dihalogen-substituted aromatic compound in Group (G2) or (G3) other than that of Group (G1) was attempted in accordance with the prior art process, it was difficult to obtain any copolymer high in polymerization degree, uniform in composition and/or good in melt stability.
As that reason, there can be mentioned the fact that the dihalogen-substituted aromatic compound of Group (G1) requires to conduct a polymerization reaction at a relatively high temperature for obtaining a polymer of high polymerization degree, while the dihalogen-substituted aromatic compound of Group (G2) is unstable and tends to decompose at such a high temperature and hence, requires to conduct a polymerization reaction at a relatively low temperature for obtaining a polymer of high polymerization degree. In addition, they are substantially different in reactivity from each other, so that any copolymers uniform in composition can not be obtained therefrom.
Besides, in the copolymerization reaction between the dihalogen-substituted aromatic compounds of Group (G1) and (G3), a homopolymer of the dihalogen-substituted aromatic compound of Group (G3) or a copolymer containing such a compound in a great amount tends to precipitate from the polymerization solvent in the initial stage of the reaction, so that any copolymers uniform in composition can not be obtained therefrom.
With a view toward improving the above-mentioned problems in the copolymerization of ##STR6## of Group (G1) with ##STR7## of Group (G2) or ##STR8## of Group (G2), the present inventors previously proposed a production process of block copolymers by forming respective prepolymers in advance and reacting these prepolymers with each other (Japanese Patent Application Nos. 248083/1989 and 342968/1989). However, it is desirable to obtain copolymers improved further in respect of polymerization degree and melt stability.
As another production process of arylene thioether polymers, there has been proposed a process in which a dihalogen-substituted aromatic compound is reacted with an aromatic dithiol or an alkali metal salt thereof (alkali thiolate) (Japanese Patent Publication Nos. I9713/1970 and 4398/1971, and Japanese Patent Laid-Open Nos. 197634/1986, 200127/1986, 529/1987, 530/1987, 91530/1987 and 20530/1987). This reaction is represented by the following two reaction formulae: ##STR9##
According to this production process, the reactivity is good. However, the aromatic dithiol and alkali thiolate of raw materials are easy to be oxidized, so that the process is accompanied by problems of difficulty in purifying and handling them, increase in production cost and difficulty in industrial practice.